BackgroundDupilumab has been used with significant benefit in the treatment of asthma and chronic rhinosinusitis with nasal polyps (CRSwNP). Phase 3 clinical trials have demonstrated transient eosinophilia and rare eosinophil-related and other adverse effects. ObjectiveTo characterize dupilumab-associated eosinophilia (absolute eosinophil count [AEC] ≥ 1.5 x 103/μL within 36 weeks of dupilumab initiation) and adverse effects associated in real-world patients with asthma and CRSwNP in the United States. MethodsRetrospective chart review of 251 patients on dupilumab for asthma and/or CRSwNP seen at a single institution. ResultsAmong the 142 patients who had AECs checked before and after treatment, 16 (11.3%) patients had post-treatment eosinophilia, including 11 (7.7%) patients who had new eosinophilia upon dupilumab initiation. Thirteen patients with post-treatment eosinophilia remained on dupilumab, 10 of whom had resolution of eosinophilia. Eosinophil-related adverse effects were rare and cases of eosinophilic granulomatous polyangiitis (EGPA) were limited to 1 patient with eosinophilia and 1 patient with normal eosinophil levels on systemic steroids. Other adverse effects included arthralgias (13/251, 5.2%), rash (8/251, 3.2%), and conjunctivitis (7/251, 2.8%). All patients with pre-treatment eosinophilia and the majority of patients with post-treatment eosinophilia received significant treatment benefit for their respiratory disease with dupilumab. ConclusionWhile dupilumab-associated eosinophilia is seen in a subset of patients, persistent eosinophilia or eosinophil-related adverse effects are rare. Furthermore, treatment benefit on dupilumab despite eosinophilia supports its continued use in both asthma and CRSwNP.